Friction welding is a type of solid-state welding process that generates heat through mechanical friction between a moving workpiece and a stationary component in combination with a lateral force that plastically displaces and fuses the materials. Friction welding may be used with a variety of metals and thermoplastics in a wide range of applications, including those in the aerospace, marine and automotive industries. Friction welding may be advantageous in some applications compared to other welding processes for a variety of reasons, including the ability to join dissimilar materials, relatively short joining times and the ability to limit heat input to the weld interface.
In one application of friction welding, referred to as friction plug welding, a tapered plug is friction welded into a tapered hole in a substrate. This welding technique may be used to repair castings or to fill holes that occur on the completion of a friction stir welding pass when a stirring probe is withdrawn from the weld.
The weld strength properties of friction plug welds along the line of the fusion may be less than desired in some applications. For example, when used to close a termination hole on a circumferential friction stir weld on a tank, the strength of the friction plug weld along its line of fusion with the parent tank material may be less than the strength of the friction stir weld.
Accordingly, it would be desirable to provide a method and apparatus for friction plug welding that exhibits improved weld strength properties.